OIL WEEP AT GASKET BETWEEN UPPER AND LOWER INTAKE. GMC Truck GMC C Sierra

SUBJECT: OIL WEEP AT GASKET BETWEEN UPPER AND LOWER INTAKE MANIFOLD (NO REPAIR AT THIS TIME)

MODELS: 1996-99 CHEVROLET AND GMC C/K, G, P MODELS 1999 CHEVROLET AND GMC MEDIUM DUTY C SERIES AND BUS CHASSIS WITH 7.4L ENGINE - (VINS B, D, J - RPOS L21, LP4, L29)

CONDITION:

OWNERS MAY COMMENT OF A WEEP OR LEAK CONDITION OCCURING AT THE GASKET BETWEEN THE UPPER AND LOWER INTAKE MANIFOLD.

CAUSE:

DURING NORMAL OPERATION, THE PCV SYSTEM DRAWS SMALL AMOUNTS OF OIL VAPOR OUT OF THE ENGINE'S CRANKCASE. THIS OIL VAPOR CAN CONDENSE AND FORM A THIN FILM INSIDE THE INTAKE MANIFOLD. WHEN THIS FILM TOUCHES THE GASKET BETWEEN THE UPPER AND LOWER INTAKE MANIFOLD, IT CAN WEEP OR WICK THROUGH THE GASKET. WHEN ENOUGH OIL WEEPS OR WICKS THROUGH THE GASKET, IT MAY APPEAR THAT THE INTAKE MANIFOLD IS LEAKING OIL, EVEN THOUGH IT IS NOT. ALSO, THE AREA BETWEEN THE CANISTER PURGE PORT AND THE EGR VALVE ON THE INTAKE MANIFOLD MAY APPEAR TO HAVE AN OIL LEAK. THIS IS CAUSED BY THE INTRODUCTION OF THE PCV INTO THE UPPER INTAKE MANIFOLD.

CORRECTION:

THERE IS CURRENTLY NO REPAIR FOR THIS CONDITION. CHANGING THE INTAKE MANIFOLD GASKET WILL ONLY PROVIDE A VERY SHORT TERM FIX. THEREFORE, NO ATTEMPT TO CHANGE THE INTAKE MANIFOLD GASKET SHOULD BE ATTEMPTED FOR THIS CONDITION. AS SOON AS A FIX IS DEVELOPED FOR THIS CONDITION THIS BULLETIN WILL BE RE-ISSUED WITH THAT INFORMATION.

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GENERAL MOTORS BULLETINS ARE INTENDED FOR USE BY PROFESSIONAL TECHNICIANS, NOT A "DO-IT-YOURSELFER". THEY ARE WRITTEN TO INFORM THOSE TECHNICIANS OF CONDITIONS THAT MAY OCCUR ON SOME VEHICLES, OR TO PROVIDE INFORMATION THAT COULD ASSIST IN THE PROPER SERVICE OF A VEHICLE. PROPERLY TRAINED TECHNICIANS HAVE THE EQUIPMENT, TOOLS, SAFETY INSTRUCTIONS AND KNOW-HOW TO DO A JOB PROPERLY AND SAFELY. IF A CONDITION IS DESCRIBED, DO NOT ASSUME THAT THE BULLETIN APPLIES TO YOUR VEHICLE, OR THAT YOUR VEHICLE WILL HAVE THAT CONDITION. SEE A GENERAL MOTORS DEALER SERVICING YOUR BRAND OF GENERAL MOTORS VEHICLE FOR INFORMATION ON WHETHER YOUR VEHICLE MAY BENEFIT FROM THE INFORMATION.